Process and device for monitoring leakage from a radiant tube fired by a gas burner

ABSTRACT

A process and a device for monitoring the imperviousness of a radiant tube fired by a gas burner is disclosed. From a burner control a burner signal is derived that may have at least the states BURNER OFF when the burner is switched off and BURNER ON when the burner is switched on. In addition, the exhaust gas flow of the burner is monitored and an exhaust gas signal is derived there from which may at least have the states EXHAUST GAS OFF when there is no sufficient volume flow of exhaust gas flowing out of the radiant tube, and EXHAUST GAS ON when there is a correctly flowing exhaust gas. The burner signal and the exhaust gas signal are linked with each other for outputting a failure signal in case the combination BURNER ON and EXHAUST GAS OFF results.

BACKGROUND OF THE INVENTION

[0001] The invention relates to a process and device for monitoring the imperviousness of a radiant tube fired by a gas burner.

[0002] Ceramic radiant tubes fired by gas burners are being more and more used in particular within industrial furnaces, due to their long operating life.

[0003] A disadvantage when using ceramic radiant tubes rests in the fact that in case of a breakdown the radiant tube cracks and instantly a large free cross section to the furnace room exists. Up to now a breakdown of the radiant tube cannot be easily detected and may lead to considerable disadvantages within the process, since the furnace atmosphere is modified accordingly. Also there are considerable safety problems.

[0004] In case the industrial furnace comprises several radiant tubes, then a breakage cannot be immediately detected. Usually, the furnace cavity is not be sealed by its inlet and outlet with respect to the outer environment so that there is no pressure increase. If the furnace is filled with protective gas, then the atmosphere is modified in case of a radiant tube breakdown which may develop gradually and which can only be detected by continuous analyses or other measuring methods. In addition, it cannot be directly detected which radiant tube is broken. A localization is only possible by switching off the respective burner of the radiant tube. This is time consuming, since it has to be waited for a reaction of the furnace atmosphere or of an outcome thereof, respectively. Also, analyses of protective gas components of the radiant tube may be very time consuming. If the furnace cavity is only filled with air, then a radiant tube breakage is hardly detectable within a production process.

[0005] All these problems are a disadvantage when using ceramic radiant tubes. By contrast, radiant tubes made of steel are subject to an increased corrosion and are less temperature resistant. Also failures of steel radiant tubes usually develop gradually.

[0006] From U.S. Pat. No. 4,219,324 it is known to monitor the operating of a burner by means of flame detector. In addition, herein the composition of the exhaust gas flow is monitored to detect a failure state in case of a deviation from preset values.

[0007] From U.S. Pat. No. 4,508,501 also a method of monitoring the imperviousness of a radiant tube fired by a gas burner is known, wherein the oxygen content within the exhaust gas flow of the burner is monitored by a burner control. In case of a deviation from a preset value, a failure signal is generated.

[0008] Finally, from JP-A-55 066 729 (Patent Abstracts of Japan) it is also known to monitor the exhaust gas flow of the burner and to generate a signal there from for monitoring. Also herein the exhaust gas composition is monitored.

[0009] In the prior art a monitoring of the imperviousness of a radiant tube requires a tedious monitoring of the gas composition which is complicated and expensive and also bears the problem of sensor aging.

SUMMARY OF THE INVENTION

[0010] Thus, it is a first object of the invention to disclose a process and a device for monitoring leakage from a radiant tube fired by a gas burner having a simple and cost effective design.

[0011] It is a second object of the invention to disclose a process and a device for monitoring leakage from a radiant tube that can easily be adapted to different types of radiant tubes.

[0012] It is a third object of the invention to disclose a process and a device for monitoring leakage from a radiant tube that allows a reliable monitoring of the imperviousness of the tube also over a long operating time without aging problems related to sensors and the like.

[0013] It is a forth object of the invention to disclose a process and a device for monitoring leakage from a radiant tube that provide a fast response in case of a failure.

[0014] These and other objects of the invention are solved by a process for monitoring leakage from a radiant tube fired by a gas burner, wherein the on/off state of the burner is monitored and a burner signal indicative for the on/off state is generated which may at least have the state BURNER OFF when the burner is switched off and BURNER ON when the burner is switched on, wherein in addition the exhaust gas flow of the burner is monitored and an exhaust gas signal is derived there from which may at least have the states EXHAUST GAS OFF when there is no sufficient volume flow of effluent exhaust gas, and EXHAUST GAS ON in case of suitably flowing exhaust gas, and wherein the burner signal and the exhaust gas signal are linked with each other to generate a failure signal in case of an inadmissible combination of the burner signal and the exhaust gas signal.

[0015] In addition, the object of the invention is solved by a device for monitoring the imperviousness of a radiant tube fired by a gas burner comprising a sensor for monitoring the exhaust gas flow of the burner generating a characteristic exhaust gas signal indicative for exceeding a preset threshold value, and further comprising a monitoring circuitry into which the exhaust gas signal and a burner signal indicative for the on/off state of the burner are fed and which generates a failure signal in case of an inadmissible combination of the burner signal and the exhaust gas signal.

[0016] The invention is completely solved in this way.

[0017] If the burner is switched on, which is indicated by the burner signal, then the exhaust gas flowing out of the radiant tube must flow with an exhaust gas volume flow which is characteristic for the burner. In case the exhaust gas volume flow is not existent or does not have the necessary value, then an imperviousness of the radiant tube can be deducted there from. By linking the exhaust gas signal which is indicative for a sufficient volume flow of the exhaust gas with the burner signal in this way, an imperviousness of the radiant tube can easily be detected.

[0018] The burner signal may be derived from the on/off switch of the burner, in case only the on/off state shall be indicated. However, preferably the signal is derived from a burner control device which usually does not only indicate the switched on state of the burner, but also monitors a correct operation of the burner, this being indicated by a signal BURNER ON. Alternatively, it is possible to provide a separate monitoring device being configured as a sensor, e.g. a flame sensor, for generating the burner signal.

[0019] The monitoring of the exhaust gas flow can be performed by a volumetric measurement, by an effective pressure measuring, by a flow velocity measuring using an inductive method or an ultrasonic method or a pressure probe method.

[0020] A particularly simple design results, if the exhaust gas flow is monitored by means of an effective pressure measuring using a flow constriction by a throttle device, in particular by a differential pressure disk. Then a differential pressure measurement between the inlet and the outlet of the throttle device can be performed. In case the measured differential pressure falls below a preset threshold range, then the received exhaust gas signal is set to EXHAUST GAS OFF. In case the pressure differential is larger, then the exhaust gas signal is set to EXHAUST GAS ON.

[0021] The threshold value between the inlet and the outlet of the differential pressure disk may be set to a value of 10 mbar, preferably of 5 mbar, more preferably of 3 mbar, in particular of 2 mbar.

[0022] According to an additional development of the invention, also a failure signal is generated with the combination BURNER OFF and EXHAUST GAS ON.

[0023] Namely, when there is detected an exhaust gas signal of a sufficient level without the existence of the signal BURNER ON which is characteristic for the switched on burner, then it can be deducted that such a high volume flow is generated by an exhaust gas vent and sucked from the impervious radiant tube out of the furnace, so that the signal EXHAUST GAS ON is generated.

[0024] In addition, also a monitoring can be performed when the burner is switched off and operates in cooling operation for the radiant tube for cooling the furnace cavity, wherein preferably the coolant air is the air which is used for combustion during burner operation. To this end, also a vent may provide the coolant air which also operates when the burner is switched off. Possibly, also a separate coolant air line may be mounted to the burner delivering additional coolant air into the radiant tube to allow an increased furnace cooling.

[0025] The operation of the coolant air and possibly also of the additional coolant air can be monitored and a coolant air signal and possibly an additional coolant air signal derived there from can be linked with the exhaust gas signal to output a failure signal in case of an inadmissible combination.

[0026] It will be understood that the above-mentioned and following features of the invention are not limited to the given combinations, but are applicable in other combinations or taken alone without departing from the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Further features and advantages of the invention will become apparent from the following description of preferred embodiments taken in conjunction with the drawings. In the drawings show:

[0028]FIG. 1 a simplified representation of an industrial furnace comprising a burner and a radiant tube designed as a jacketed radiant tube, and further comprising an assigned device for monitoring the imperviousness of the radiant tube; and

[0029]FIG. 2 a possible embodiment of a circuitry comprising a lighted key for indicating and for acknowledging a signal indicative for the leakage of the radiant tube.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] In FIG. 1 an industrial furnace heated by a gas fired radiant tube and equipped with a monitoring device according to the invention for monitoring the imperviousness of the radiant tube is shown schematically and designated in total with numeral 10.

[0031] The industrial furnace 10 comprises a furnace cavity which is merely indicated by a dash dotted line and heated by a gas burner 12. The gas burner 12 comprises a radiant tube 14 protruding into the furnace cavity 11 and being designed as a jacketed or sheathed radiant tube. The exhaust gases guided back via the radiant tube 14 pass through an outlet 14 (shown merely schematically) into an exhaust gas line 18 and are guided into an exhaust gas channel 20.

[0032] Now according to the invention, for monitoring the imperviousness of the radiant tube 14, the exhaust gas flow flowing via the exhaust gas line 18 is monitored and is linked with a burner signal derived from the burner control 28 which is indicative for a correct operation of the burner. If the burner operates correctly and if there is no exhaust gas flow having the characteristic value for the type of burner that is used, then it can be concluded that there is a leakage of the radiant tube.

[0033] To this end, a differential pressure disk 22 is introduced into exhaust gas line 18. A pressure measuring device 24 is connected via measuring lines 26 to the inlet and outlet of the pressure differential disk, namely directly before and thereafter. In case a pressure differential Δp of sufficient value, e.g. 2 mbar, results while the burner 12 is operating correctly, then it can be deducted that there is no leakage of the radiant tube 14. If this is not the case, then a failure signal is generated. To this end, a monitoring circuitry is provided which is merely schematically depicted by numeral 38. The monitoring circuitry 38 is fed with the exhaust gas signal 38 received from the differential pressure measurement device 24 and with the burner signal 32 derived from burner control 28. The monitoring circuitry 38 generates an output signal 36 which, in the simplest case, can merely have the states OK or FAILURE.

[0034] The exhaust gas signal 34 received from pressure measuring device 24 also may only have the states EXHAUST GAS ON or EXHAUST GAS OFF in the simplest case. Moreover, the burner gas signal 32 preferably is a binary signal which can only have the states BURNER ON and BURNER OFF.

[0035] It will be understood that the linkage of the exhaust gas signal 34 and the burner signal 32 can easily be performed by a common permanently wired circuit or by a digital switching logic which, in the simplest case, e.g. may be designed using of TTL logic elements.

[0036] In the latter case, the output signal 36 depending from the different possible combinations of the burner signal 32 and the exhaust gas signal 34 could then be represented in a Boolean operation table, such as subsequently shown in Table 1. TABLE 1 Exhaust Burner gas Output signal signal signal State 0 0 0 0 1 0 (1) 1 0 1 1 1 0

[0037] Herein a “0” represents the state OFF or LOW, respectively, with respect to the input signals, i.e. BURNER OFF or EXHAUST GAS OFF, respectively, and a “1” represents the state ON or HIGH, respectively, i.e. BURNER ON or EXHAUST GAS ON, respectively.

[0038] With respect to the output signal a “0” represents the state CORRECT or OK, respectively, while a “1” represents a failure.

[0039] In the simplest embodiment of the circuitry only for the combination BURNER ON and EXHAUST GAS OFF a failure signal is generated, i.e. a logical “1” is output. According to an alternative design, in addition also for the combination BURNER OFF and EXHAUST GAS ON a failure signal is output which is indicated by the logical “1” shown in brackets for this combination.

[0040] Namely, in the latter case it must be concluded that with a broken radiant tube such a high volume flow is sucked out of the furnace cavity by means of an exhaust gas vent, that the signal EXHAUST GAS ON is generated.

[0041] If the burner and the radiant tube associated therewith are also utilized for cooling furnace cavities which can be done using the coolant air (combustion air) and/or using additional coolant air guided via a coolant air line attached separately to the burner, then also in this case a monitoring can be performed.

[0042] For cooling simply the coolant air flow (combustion air volume flow) can be utilized which is also present when the burner is not switched on. Again this can be monitored by means of a differential pressure measurement to generate a signal COOLANT AIR ON or COOLANT AIR OFF, respectively, this being indicative for the present flow of coolant air or for the missing flow of coolant air, respectively. In a corresponding manner also the flow of additional coolant air can be monitored to derive a signal ADDITIONAL COOLANT AIR ON or ADDITIONAL COOLANT AIR OFF, this being indicative for a flow of additional coolant air or for a missing flow of additional coolant air, respectively.

[0043] In addition to Table 1, Table 2 lists possible combinations which may result during coolant operation when the burner is switched off. Herein, in a manner corresponding to Table 1, the coolant air signal represented by a “1” (“0”) represents the signal COOLANT AIR ON (COOLANT AIR OFF) and with respect to the additional coolant air signal a “1” (“0”) represents the signal ADDITIONAL COOLANT AIR ON (ADDITIONAL COOLANT AIR OFF). TABLE 2 Additional Coolant coolant Exhaust Burner air air gas Output signal signal signal signal signal 0 1 0 1 0 0 1 0 0 1 0 1 1 1 0 0 1 1 0 1 0 0 1 1 0 0 0 1 0 1

[0044] It will be understood that the monitoring of the imperviousness of a radiant tube indicated merely schematically in FIG. 1 and in Tables 1 and 2, cannot only be performed with respect to a single furnace comprising a single radiant tube, but also with respect to furnaces comprising several radiant tubes. To this end, a pressure monitoring may be performed with respect to each radiant tube, and the exhaust gas signals received may be linked with the respective burner signals by means of individual monitoring circuitries or by means of a single monitoring circuitry.

[0045] It will be further understood that the process and the device according to the invention can be used for monitoring any kind of radiant tubes. Thus, e.g. sheathed radiant tubes, P radiant tubes and double-P radiant tubes can be monitored. The principle according to the invention can also be utilized in combination with lead-through radiant tubes and U-shaped radiant tubes. Herein the exhaust gas flow is monitored at the output of the U-tube by means of a differential pressure disk and the differential pressure measuring device.

[0046] A possible embodiment of the monitoring circuitry 38 shown in fixed wired representation using common components as shown in FIG. 2. This monitoring circuitry 38 merely outputs a failure signal when the combination BURNER ON and EXHAUST GAS OFF is received. However, in addition an illuminated key is provided for displaying and acknowledging the failure message.

[0047] The monitoring circuitry 38 may e.g. be provided in a separate housing which may in addition be attached to the respective burner.

[0048] The monitoring circuitry 38 comprises an input port 56 for the burner signal (phase signal 220 V), which may have states BURNER ON or BURNER OFF. This input port 56 is connected to a relay K1 which, at its other end, is connected with its control circuit 40 to the neutral line N via a port 64. Also to the neutral line N a relay K2 is connected with its control circuit 42 which is in line with the closing contact 41 of relay K1 and in line with the pressure measuring device 24 being connected via lines 58 and 60 and via a line 50 to the phase power line 220 V being connected via the port 62. The pressure measuring device 24 opens the opening contact shown schematically in FIG. 2, if the pressure differential exceeds the preset threshold value e.g. by 2 mbar.

[0049] In parallel to the control circuit 42 of the relay K2 an indicator lamp 44 is connected with its one end to the neutral line and with its other end via the control circuit 43 of relay K2 and a key 46 to line 50 and to port 62 and also to the 220 V phase line. Using a line 48 between control circuit 42 and the switching circuit 43 of the relay, the indicator lamp 44 is connected in parallel to control circuit 42 of relay K2.

[0050] In case the burner signal BURNER ON is received and the exhaust gas signal is absent, e.g. the opening contact of the differential pressure measurement device 24 does not open the connection between the switching circuit 41 of relay K1 and line 50, then this will be indicated by illuminating indicator lamp 44, and a failure signal is output to port 66. The failure signal may then be acknowledged by means of the key 46. 

What is claimed is:
 1. A process for monitoring leakage from a radiant tube fired by a gas burner, comprising the steps of: controlling an on/off state of the burner for generating a burner signal comprising at least the states BURNER OFF and BURNER ON, the state BURNER ON being indicative for a switched on burner and the state BURNER OFF being indicative for a switched off burner; monitoring an exhaust gas flow exiting from the burner and generating an exhaust gas signal comprising at least the states EXHAUST GAS OFF and EXHAUST GAS ON, the state EXHAUST GAS OFF being indicative for an exhaust volume gas flow falling below a certain threshold, the state EXHAUST GAS ON being indicative for an exhaust gas volume exceeding said threshold, said monitoring being performed by monitoring a pressure differential occurring between an input and, an output side of a flow constriction arranged within the flow to be monitored; comparing each detected combination of said burner and said exhaust gas signals to a set of allowed combinations; and generating a failure signal, if any of said detected combinations of said burner and said exhaust gas signals deviates from said set of allowed combinations.
 2. A process for monitoring leakage from a radiant tube fired by a gas burner, comprising the steps of: controlling an on/off state of the burner for generating a burner signal comprising at least the states BURNER OFF and BURNER ON, the state BURNER ON being indicative for a switched on burner and the state BURNER OFF being indicative for a switched off burner; monitoring an exhaust gas flow exiting from the burner and generating an exhaust gas signal comprising at least the states EXHAUST GAS OFF and EXHAUST GAS ON, the state EXHAUST GAS OFF being indicative for an exhaust volume gas flow falling below a certain threshold, the state EXHAUST GAS ON being indicative for an exhaust gas volume exceeding said threshold; comparing each detected combination of said burner and said exhaust gas signals to a set of allowed combinations; and generating a failure signal, if any of said detected combinations of said burner and said exhaust gas signals deviates from said set of allowed combinations.
 3. The process of claim 2, wherein said burner signal is derived from a control controlling an operation of said burner.
 4. The process of claim 2, wherein a failure signal is generated, if the signals BURNER ON and EXHAUST GAS OFF are detected.
 5. The process of claim 2, further comprising a feeding of a certain flow of coolant air to said radiant tube for cooling a furnace room heated by said radiant tube, wherein said process further comprises the following steps: monitoring said flow of said coolant air for generating a coolant air signal, said coolant air signal comprising at least the states COOLANT AIR ON and COOLANT AIR OFF, the state COOLANT AIR ON being indicative for a flow of coolant air being above a certain threshold value, the state COOLANT AIR OFF being indicative for a coolant air flow being below a certain threshold value; comparing each combination of said coolant air signal and said burner signal with a set of allowed combinations; and generating a failure signal, if any of said combinations of said burner and said exhaust gas signals deviates from said set of allowed combinations.
 6. The process of claim 5, wherein additional coolant air for cooling said furnace room is fed to said radiant tube, wherein said process further comprises the following steps: monitoring said flow of additional coolant air for generating an additional coolant air signal, said additional coolant air signal comprising at least the states ADDITIONAL COOLANT AIR ON and ADDITIONAL COOLANT AIR OFF, the state ADDITIONAL COOLANT AIR ON being indicative for a flow of additional coolant air being above a certain threshold value, the state ADDITIONAL COOLANT AIR OFF being indicative for an additional coolant air flow being below a certain threshold value; comparing each combination of said coolant air signal, said additional coolant air signal, and said burner signal with a set of allowed combinations; and generating a failure signal, if any of said combinations of said coolant air signal, said additional coolant air signal, and said burner signal deviates from said set of allowed combinations.
 7. The process of claim 2, wherein said monitoring of said flow is performed by a method selected from the group formed by volumetric measuring, pressure measuring, differential pressure measuring and flow velocity measuring.
 8. The process of claim 2, wherein a failure signal is generated in case a combination BURNER OFF and EXHAUST GAS ON is detected.
 9. A device for monitoring leakage from a radiant tube fired by a gas burner, said device comprising: a burner control device generating a burner signal comprising at least the states BURNER OFF and BURNER ON, the state BURNER ON being indicative for a switched on burner and the state BURNER OFF being indicative for a switched off burner; a flow monitoring device for monitoring an exhaust gas flow emerging from said burner and for generating an exhaust gas signal, said exhaust gas signal comprising at least the states EXHAUST GAS ON and EXHAUST GAS OFF, the state EXHAUST GAS OFF being indicative for said exhaust gas flow falling below a certain threshold, the state EXHAUST GAS ON being indicative for said exhaust gas flow exceeding said threshold; and a monitoring circuitry connected to said burner control device and said flow monitoring device for receiving said burner signal and said exhaust gas signal, said monitoring circuitry being configured for comparing each detected combination of said exhaust gas and said burner signals with a set of allowable combinations and for generating a failure signal, if any of said detected combinations deviates from said set of allowable combinations.
 10. The device of claim 9, wherein said flow monitoring device is selected from the group formed by a volumetric measuring device, a pressure measuring device, a differential pressure measuring device and a flow velocity measuring device.
 11. The device of claim 10, wherein said radiant tube comprises an outlet through which said exhaust gas emerges, and wherein a flow restriction having an input side and an output side is connected with its input side to said outlet, wherein said monitoring device further comprises a differential pressure detector for measuring the pressure differential between said input and said output sides of said flow restriction.
 12. The device of claim 10, wherein said monitoring circuitry is configured for generating a failure signal upon detecting a combination of said burner and exhaust gas signals comprising the states BURNER ON and EXHAUST GAS OFF. 